on the Action of Wetter and Air on Lead, 83 



much resembled some brilliant varieties of mica: under the 

 microscope by transmitted light they were yellowish. 



7. Such are the general appearances presented by the action 

 of water on lead. To ascertain whether any effect was produced 

 when access of air was entirely cut off, I filled a little retort 

 with distilled water, and boiled it for some time; I then intro- 

 duced into it some fresh-cut clear slips of lead. The beak of 

 the retort, which was quite full of water, was then immersed 

 in a basin of mercury, the surface of which was covered with 

 water. When this arrangement was examined after standing 

 three weeks, not the smallest bubble of gas was visible. The 

 lead was still bright, though a little whitish in places : the 

 water struck a very pale brown when tested by sulphuretted 

 hydrogen. The retort was then left open and half-filled for 

 a night ; a quantity of the white substance formed, and the 

 water gave a deep brown when tested. It is evident from this 

 experiment that the lead does not derive oxygen from the 

 water, but from the air contained in it, though, like iron in si- 

 milar circumstances, it is a delicate test for oxygen dissolved 

 in water*. 



8. To obtain the products of the action of air and water 

 on lead in larger quantities, I filled a quart bottle about f rds 

 of its capacity with distilled water, which I agitated briskly 

 with the air, and introduced a parcel of clean cuttings of sheet 

 lead : white clouds appeared in a few minutes; and the bril- 

 liant grey crystals (b) began to be visible on the surface of 

 the lead after standing four days. After, standing a month, 

 the surface of the water was covered by a slightly coherent 

 stratum of the white crystalline substance, and there was also 

 a deposit of the same matter : the lead was covered by the 

 brilliant grey crystals. A quantity of these last were brushed 

 off the lead : they dissolved quietly in acetic acid. A portion 

 introduced into a bit of glass tube, closed at one end and pre- 

 viously counterpoised, weighed y 9 ^ grain. When this was 

 heated red by a spirit-lamp, it decrepitated a little, and a very 

 small portion of water was condensed in the cool part of the 

 tube : when this was driven off, the loss was only y^ of a grain. 

 The substance had become yellow, but the structure was not vi- 

 sibly altered. In another trial no water was given off. Hence 

 it appears that this product was the anhydrous protoxide of 

 lead. But I found that besides these laminar crystals there were 

 many much smaller crystals adhering to the lead : when ex- 

 amined by the microscope they appeared colourless and semi- 

 transparent, having very brilliant facets. Many of them were 



* See Dr. M. Hall on the Oxidation of Iron, Journal of Science, vol. vii. p. 55. 



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